It is often desirable to perform a biopsy to sample selected tissue from a patient for medical evaluation. For example, biopsies can be useful in diagnosing various forms of cancer and other diseases affecting a localized area of tissue. Traditional notched stylet biopsy needles comprise an inner stylet having a lateral-facing specimen notch slidably disposed within an outer cutting cannula. In typical use, the inner stylet is inserted into tissue to be sampled and, after a tissue specimen has prolapsed into the specimen notch, the outer cutting cannula is fired over the stylet. The sharpened distal end of the cutting cannula severs the captured tissue specimen from the surrounding tissue and holds it within the notch of the stylet. Commercially-available notched stylet biopsy needles often come with different throw lengths, such as 10 mm or 20 mm, where the throw length refers to a longitudinal length of the notch exposed before the cutting cannula is fired, and consequently also refers to the approximate length of the sample obtained.
In traditional notched-stylet biopsy needles, the inner circumference of the cutting cannula is typically circular, and the cross section of the specimen notch of the stylet is either semi-circular or C-shaped. Because of the cross-sectional area taken up by the stylet, the amount of tissue captured in the notch is necessarily significantly less than the full cylindrical volume, or “full core,” defined by the outer cannula. Typically, the tissue sample obtained is characterized by a cross section that is asymmetrically truncated relative to the full circular core of the cutting cannula. If the notch is not facing toward the tissue of interest, than an incorrect sample may be initially obtained. Thus, in order to obtain a suitable amount of tissue for medical evaluation, it can be necessary to take multiple biopsy samples or to use needles with longer throw lengths.
Moreover, the performance of some notched stylets can suffer due to inadequate strength or stability. For example, commercially-available notched stylets can have a tendency to bend or deflect as they penetrate tissue, which can adversely affect the quality of the sample taken. Because increasing the throw length (i.e. extending the thinner notched portion) generally leads to a decrease in the rigidity of the stylet, the risk of sample inadequacy or unsuitability due to unwanted deflection of the stylet generally increases when longer throw lengths are used. Further, increasing the amount of tissue obtained by increasing depth of the notch is not indicated for traditional needles for several reasons. If the notch depth is to be increased, either the overall size of the stylet and its cannula must be increased, or more of the stylet must be removed to form the notch, or both. However, increasing overall size can increase the discomfort for the patient and difficulty in inserting the needle through potentially dense tissue. Removing more of the stylet results in a stylet more prone to the bending or deflection noted above.
While existing partial core products can be effectively used, there is a need for a biopsy device that addresses existing problems and can obtain a tissue sample having a cross section that is larger and more symmetrical relative to the overall cross section of the device, while being easier and more inexpensive to manufacture than existing “full core” needles and being as or more reliable than existing partial core needles.